This invention relates to surveillance radar and more particularly to a method and apparatus for distinguishing between wanted and unwanted moving targets.
Surveillance radars have historically had difficulty distinguishing desired moving targets such as aircraft from undesired moving targets such as birds. The apparent radar cross section (RCS) of wanted targets is often less than the RCS of unwanted targets due to target fluctuations, multipath, radar antenna patterns and the size of aircraft and missiles. Techniques such as moving target indication (MTI) are insufficient to distinguish unwanted targets from wanted targets because the radial velocities (i.e., the component of velocity in the direction of the radar) of the unwanted targets often equal or exceed the ambiguous radial velocity of the desired targets.
The primary means of rejecting unwanted targets in surveillance radars have been the use of sensitivity time control (STC), two-beam antenna techniques (which assume that unwanted targets are near the earth's surface) and clutter maps. These techniques are described in "Radar Handbook" by Merrill Skolnik, Editor in Chief, second edition, McGraw-Hill Publishing Company, 1990, pp. 15.6514 15.70. Although each of these techniques provides some mitigation of the unwanted target problem, each has sufficient shortcomings to prevent achieving a desired performance level. An alternative method of eliminating unwanted targets in fire control radars is to eliminate all targets with absolute radial velocities below some value such as 120 knots. However, this solution is not available to surveillance radars with relatively low ambiguous velocities which are typically around 80 knots.